Our research in molecular cytogenetics has the overall goal of understanding what DNA sequences are relevant to gene expression during the normal development of an organism. In particular the research described here has two goals. The first is to perfect our existing method for the resolution and display of single restriction segments from Drosophila DNA to a point where it is a usable laboratory procedure. The immediate prospect is to identify and recover genomic DNA segments from regions covered by multiple duplications in strains of flies that have been genetically constructed for this purpose. This may open the way to recover any genetically defined region of the genome and in particular those genes for which there is no prospect of obtaining DNA or RNA probes. If straightforward improvements in our methods are made, they should be applicable to the analysis of human genomes and those of various mammalian cell lines. In this case these restriction karyotypes would be useful in the study of human genetics, development, ageing and tumorous transformation. The second goal is to perfect and improve a functional assay for Drosophila DNA by injecting early mutant embryos with wild type DNA and observing the expression of the wild type gene in the mutant embryo or adult. The first experiments will deal with the genes rosy and vermillion and the goal will be to purify the genomic DNA segment that confers wild type phenotype - a kind of Drosophila transformation system. Other experiments will deal with the detection of XDH (the gene product of the rosy locus) by a microenzymological assay of the injected embryo or larvae. In this way we plan to identify and map the DNA molecule carrying the rosy locus and to determine what parts of the sequence are relevant to gene expression. With improved efficiency of transformation, one can expect germ-line transformations as well. In this case, the way would be open to continue the study of any gene using both molecular and classical genetic techniques.